Charged particle beam exposure method and apparatus

ABSTRACT

A charged particle beam exposure method for deflecting a charged particle beam in a deflection system which includes electromagnetic deflection coils, includes the steps of (a) controlling the deflection system based on deflection data, and (b) generating heat at least a vicinity of the electromagnetic deflection coils so as to compensate for a change in heat generated from the electromagnetic deflection coils.

BACKGROUND OF THE INVENTION

The present invention generally relates to charged particle beamexposure methods and apparatuses, and more particularly to a chargedparticle beam exposure method which is suited for realizing a highresolution electron mean exposure at a high throughput, and to a chargedparticle beam exposure apparatus which employs such a charged particlebeam exposure method.

Recently, there is much attention on exposure techniques using a chargedparticle beam such as an electron beam because of the need to accuratelyexpose extremely fine patterns to meet the increasing integrationdensity of semiconductor integrated circuit devices. In order to realizea high throughput, the charged particle beam is shaped into a beamhaving an arbitrary cross sectional shape and the shaped beam isirradiated on a wafer. It is desirable that the numerical aperture islarge in order to realize a high resolution, and it is desirable thatthe charged particle beam travels a short distance to the wafer so as toreduce the Coulomb interactions of the charged particle beam. For thesereasons, an optical system of the charged particle beam has a shortfocal distance.

An electron beam exposure apparatus normally uses an electron beam whichis shaped to have a rectangular cross section or a cross section havingan arbitrary shape, and the shaped electron beam draws the pattern onthe wafer. FIG. 1 shows the column structure of an example of aconventional electron beam exposure apparatus.

FIG. 1 shows a cross sectional view of the column structure in avicinity of the wafer. An electron beam EB travels from the top tobottom along an optical axis O, and is irradiated on a wafer W. Anelectromagnetic lens is provided to converge the electron beam EB on thewafer surface. The electromagnetic lens includes an electromagnetic lenscoil LC which is coupled to an iron yoke IY, and pole pieces PP arecoupled to the tip end of the iron yoke IY.

In addition, electromagnetic deflection coils EC and electrostaticdeflection electrodes EE are provided to deflect the electron beam EB.In order to shorten the focal distance, the electromagnetic deflectioncoils EC and the electrostatic deflection electrodes EE are arranged onthe inner side of the electromagnetic lens.

In the example shown in FIG. 1, a support part S is arranged on theinner side of the electromagnetic lens, and the electromagneticdeflection coils EC are mounted on this support part S. Further, theelectrostatic deflection electrodes EE are arranged on the inner side ofthe support part S.

The electron beam EB is deflected by the electromagnetic deflectioncoils EC when deflecting the electron beam EB for a relatively largeamount on the order of several mm, for example. On the other hand, theelectron beam EB is deflected by the electrostatic deflection electrodesEE when deflecting the electron beam EB at a high speed for a relativelysmall amount on the order of 100 μm, for example.

In the case of the electron beam exposure which exposes a relativelylarge area in one exposure, the Coulomb interactions of the chargedparticles cause problems. The focal distance of the optical system isshortened in order to eliminate the limit of the resolution caused bythe Coulomb interactions. However, the deflection efficiency of thedeflector deteriorates if the focal distance is shortened. Accordingly,in the electron beam exposure system having the shortened focaldistance, a large current must be applied to the electromagneticdeflection coils EC in order to obtain a desired amount of deflection.

FIG. 2 shows a perspective view of the electromagnetic deflection coilsEC. The electromagnetic deflection coils EC have a saddle shape, and arefixed at mutually confronting positions on the outer periphery of thesupport part S. The support part S has a cylindrical shape and is madeof ceramics or the like.

According to the conventional electron beam exposure apparatus, theelectron beam EB is deflected using the electromagnetic deflection coilsEC provided in a plurality of stages, and the pattern is drawn on thewafer W by scanning the wafer surface by the deflected electron beam EB.The electromagnetic deflection coils EC are divided into two systems,that is, X and Y systems, depending on the operating direction. Theelectromagnetic deflection coils EC are coupled in series within eachsystem. The electromagnetic deflection coils EC of the two systemsreceive driving currents from independent driving circuits.

For example, a current on the order of ±2 A is required to deflect theelectron beam EB with a deflection efficiency is approximately 2.5 mm/1Ain a main deflection region which is 2 mm×2 mm. Hence, if eachelectromagnetic deflection coil EC is formed from a copper wire having adiameter of 0.5 mm, the resistance thereof becomes approximately 1.5 Ω.

In order to avoid the Coulomb interactions of the charged particle beam,it is necessary to shorten the focal distance of the optical system ofthe charged particle beam. But if the focal distance is shortened, thedeflection efficiency deteriorates, and a larger current is required ifthe same amount of deflection is to be obtained with the shortened focaldistance.

In addition, in order to operate the electromagnetic deflection coils ECat a high speed, it is necessary to reduce the inductance, and thus, itis desirable to reduce the area of the electromagnetic deflection coilsEC.

On the other hand, heat is locally generated within the column structureif the charged particle beam is processed using the electromagneticdeflection coils EC having the above described arrangement, and such ageneration of heat is unavoidable. The generated heat ranges fromseveral W to several tens of W, for example.

When the charged particle beam exposure apparatus of the type describedabove is used, the deflection position of the charged particle beam andthe focal position (or point) of the charged particle beam drift withthe operating time of the charged particle beam exposure apparatus. Itmay be regarded that the following causes the drift of the deflectionposition and the focal position of the charged particle beam.

(a) Changes in the outputs of an amplifier and a lens power source;

(b) An eddy current flowing to peripheral metal parts due to a change inthe magnetic flux generated by the deflection coils;

(c) Charge-up of parts through which the charged particle beam passes;

(d) Changes in the position and dimension of the deflection coils withtime; and

(e) Changes in the positions and dimensions of the deflection coilsthemselves, bobbins and other parts due to temperature changes caused bythe heat generated from the deflection coils.

The present inventors initially doubted the possibility that theresponse characteristic of the deflection coil greatly deterioratingwith the operating time of the charged particle beam exposure apparatus.However, the output of the amplifier had not changed, and the set timeconstant remained the same. In addition, the inductance of thedeflection coil also remained approximately the same. In other words,even though the deflection magnetic field was set, some factor changedthe beam position. But it seemed impossible for the eddy current tochange before and after the exposure when the same deflection was made.

Furthermore, the beam position on the optical axis is reproducible for along time if the charged particle beam is not deflected. For thisreason, it seemed impossible for the charge-up to cause thedeterioration of the response characteristic of the deflection coil.

The remaining possibility was the changes in the positions anddimensions of the deflection coils themselves, the bobbins and otherparts such as the pole pieces due to temperature changes caused by theheat generated from the deflection coils. As described above, the heatof several W to several tens of W may be generated from theelectromagnetic deflection coil, and the radiation effect is poor if theelectromagnetic deflection coils are arranged in a vacuum surrounding.

In the converging deflection system having the shortened focal distance,the lens magnetic pole becomes small because of the need to make thelens magnetic field strength large and the deflection magnetic fieldstrength large. Consequently, the deflection coils which are provided onthe inside must be arranged without a gap within a space which is narrowin both the direction of the optical axis and the radial direction. As aresult, the part which holes the deflection coils is made extremelythin, and the heat capacity thereof is reduced to several fractions ofthat of the conventional case.

In addition, the difference between the radii of the deflection coils inthe X and Y systems is small. But although the size of the deflectioncoil is reduced, the thickness of the wire member is approximately thesame as that of the conventional case. For this reason, the thickness ofthe deflection coil in the direction in which the wire is overlapped islarge, and the inner turns of the wire of the deflection coil arecovered by the outer turns of the wire.

For this reason, even if the outer side of the deflection coil wereair-cooled, the air-cooling effect would greatly differ between theouter turns of the wire and the inner turns of the wire. The inner turnsof the wire of the deflection coil virtually cannot be air-cooleddirectly, and the cooling is in effect made via the thermal conductionof the bobbin. Hence, the cooling effect of the inner turns of the wireand the outer turns of the wire of the coil greatly differ.

If the deflection coil were made using a thin wire member in order toimprove the air-cooling effect, the amount of heat generated from thedeflection coil would increase. As a result, the deflection accuracy ofthe charged particle beam would further deteriorate due to the thermalexpansion of the wire member itself and the thermal expansion of thebobbin on which the deflection coil is adhered.

In a case where a copper wire member is used for the deflection coil andthe bobbin is made of ceramics, positional errors of 0.34 μm and 0.16 μmmay respectively be generated in a main deflection region of 2 mm×2 mmwhen the temperature rises by 10° C., because the coefficient of thermalexpansion of the deflection coil is 1.7×10 cm⁻⁵ and the coefficient ofthermal expansion of the bobbin is 8×10 cm⁻⁶ in this case.

The deflection coil and the bobbin are actually adhered to each other,and it may be anticipated that the amount of positional error will takea value between 0.34 μm and 0.16 μm. Even if this anticipated value ofthe positional error were 0.2 μm, the positional error in the maindeflection region would be 0.4 μm at the maximum. Such a positionalerror is too large when forming patterns on the submicron order.

There is yet a bigger problem to be solved. That is, the heat generatedfrom the deflection coil causes the thermal expansion of the wire memberitself and the thermal expansion of the bobbin on which the deflectioncoil is adhered. Furthermore, the heat generated from the deflectioncoil causes thermal expansion of ferrite pole pieces which form aprojection lens. These thermal expansions change the deflectingdirection and the deflection efficiency of the deflection coil and thelens magnetic field strength, and deteriorate the accuracy of thedeflection position. The thermal expansion of the magnetic pole inparticular introduces an error in the origin of the deflectioncoordinate and a focal error.

Particularly in the case of an exposure which is made while a stagecarrying the wafer continuously moves, an alignment mark on the wafer isdetected prior to the exposure and the exposure is started afterdetermining correction coefficients for the exposure. For this reason,the deterioration of the accuracy of the exposure position, the error inthe origin of the deflection coordinate and the focal error which occurduring the exposure are fatal to the quality of the exposure.

FIG. 3 shows measured results of deviation components of the beamposition when the main deflector is caused to generate heatcontinuously. In FIG. 3, (A) is a graph showing the change of the amountof error of the offset position with time, (B) is a graph showing thechange of the positional error in the rotation direction with time, and(C) is a graph showing the change of the positional error in the gaindirection with time.

When the main deflector is caused to generate heat continuously, theseamounts of errors will change up to large values as indicated by dottedlines in FIG. 3. As may be seen from FIG. 3, these amounts of errors arefatal to the exposure apparatus which exposes patterns of the submicronorder.

Accordingly, it is conceivable to cool the electromagnetic deflectioncoils which form the main deflector, so as to prevent the drift bysuppressing the heating. The present inventors actually madeelectromagnetic deflection coils having a large cooling capacity andstudied the results.

The tested electromagnetic deflection coil employed a double-structurebobbin which is made up of an inner bobbin and an outer bobbin tosupport the electromagnetic deflection coil. The wire member of theelectromagnetic deflection coil was wound in the radial direction in onelayer and overlapped in the rotating direction in an arcuate manner toform a desired number of coil turns. The electromagnetic deflection coilwas then bent along a cylindrical surface in the form of a saddle shape.

In addition, saddle shape coils having different radii of curvatureswere made. The coil having the smaller radius of curvature was fixed onthe outer circumference of the inner bobbin, and the coil having thelarger radius of curvature was fixed on the inner circumference of theouter bobbin. A space was formed between the inner and outer coils so asto form a passage for flowing a coolant in the direction of the opticalaxis.

The bobbin was formed to a structure which is independent or integral tothe plurality of stages of the coils, and was made of a materialincluding quartz as the main component and having a small coefficient oflinear expansion. Pure water or He gas was used as the coolant, and thecoolant was forcibly circulated.

The electromagnetic deflection coils of the main deflector were cooledefficiently by the above arrangement, so as to reduce the thermalconduction to the parts such as the pole pieces. It was thought that thetemperature rise of the structure will be extremely small by theefficient radiation.

The positional changes in the electron beam for the case where the abovedescribed electromagnetic deflection coils are used are indicated bysolid lines in FIG. 3. In FIG. 3, a curve f1 in (A) shows the amount oferror of the offset position as a function of time when the cooling wasmade, a curve f2 in (B) shows the positional error in the rotatingdirection as a function of time when the cooling was made, and a curvef3 in (C) shows the positional error in the gain direction as a functionof time when the cooling was made.

However, as may be seen from FIG. 3, even though the electromagneticcoils were cooled, the changes in the beam position were only reduced toone half of the case where no cooling was made.

For example, the amount of error of the offset position wasapproximately 0.5 μm after approximately 3 minutes from the start of theexposure when no cooling was made. But even when the cooling was made,the amount of error in the offset position was only reduced toapproximately 0.3 μm. The amount of error of the offset positiongradually saturated with time, and the amount of error was approximately0.4 μm after the saturation which was not within a tolerable range.

In addition, compared to the case where no cooling was made, thepositional error in the rotation direction was only reduced toapproximately one-half even when the cooling was made. The reduction ofthe positional error in the gain direction by making the cooling waseven smaller compared to the case where no cooling was made.

In other words, even though the cooling efficiency improved with respectto the heat generation, it was evident that the cooling was incompleteand that the temperature change in the structure occurred due to theheat generation. It is conceivable to increase the cooling capacity ofthe coolant so that the amount of heat generated can be neglected, butthere is a possibility of introducing mechanical vibration or the likedue to the increased flow rate if the flow rate of the coolant isincreased. On the other hand, there is a limit to increasing the flowrate of the coolant. It is also conceivable to further reduce thethermal conduction from the electromagnetic deflection coils to the polepieces and the like, but there is of course a limit to doing this.

The temperature rise of the pole pieces with respect to the generationof heat by the electromagnetic deflection coils was also measured. Itwas found that the temperature rise is approximately 1.5° C. in 10minutes when no cooling was made and approximately 0.3° C. in 10 minuteswhen the cooling was made. The temperature rise saturated inapproximately 10 minutes, and the saturation values greatly differbetween the case where no cooling is made and the case where the coolingis made. That is, the cooling effect can be seen.

However, the cooling effect is far from sufficient for the purpose ofsatisfactorily improving the accuracy of the exposure system. Thetemperature change in the initial stage in particular is not very large,and the cooling effect within the time of approximately 3 minutes fromthe start of the exposure is not very notable with respect to the driftof the beam position.

In order to obtain the high accuracy required by the semiconductorintegrated circuits, the tolerable range of the temperature change ofthe structure due to the heat generated by the main deflector should beless than 0.1° C. However, the cooling described above cannot realizesuch a small tolerable range.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful particle beam exposure method .and apparatus in whichthe problems described above are eliminated.

Another and more specific object of the present invention is to providea charged particle beam exposure method for deflecting a chargedparticle beam in a deflection system which includes electromagneticdeflection coils, comprising the steps of (a) controlling the deflectionsystem based on deflection data, and (b) generating heat at least in avicinity of the electromagnetic deflection coils so as to compensate fora change in heat generated from the electromagnetic deflection coils.According to the charged particle beam exposure method of the presentinvention, it is possible to prevent the position and dimension of partssuch as pole pieces from changing due to thermal expansion even if theheat generated from the electromagnetic deflection coils changes. Forthis reason, it is possible to always stably determine the beam positionand the focal position. As a result, it is possible to draw extremelyfine patterns with a high accuracy. The charged particle beam exposuremethod of the present invention can prevent the change in the beamposition based on the deflection of the charged particle beamparticularly in a charged particle beam exposure apparatus which has adeflection system with a relatively short focal distance. In addition,the accuracy of the exposure can be guaranteed regardless of theoperating time of the charged particle beam exposure apparatus, and thethroughput can be improved considerably.

Still another object of the present invention is to provide a chargedparticle beam exposure apparatus comprising a deflection systemincluding electromagnetic deflection coils for deflecting a chargedparticle beam, heat source means arranged in a vicinity of theelectromagnetic deflection coils for generating heat, and control meansfor controlling the heat source means based on currents applied to theelectromagnetic deflection coils, so as to compensate for a change inheat generated from the electromagnetic deflection coils by the heatgenerated from the heat source means. According to the charged particlebeam exposure apparatus of the present invention, it is possible toprevent the position and dimension of parts such as pole pieces fromchanging due to thermal expansion even if the heat generated from theelectromagnetic deflection coils changes. For this reason, it ispossible to always stably determine the beam position and the focalposition. As a result, it is possible to draw extremely fine patternswith a high accuracy. The charged particle beam exposure apparatus ofthe present invention can prevent the change in the beam position basedon the deflection of the charged particle beam particularly when thedeflection system has a relatively short focal distance. In addition,the accuracy of the exposure can be guaranteed regardless of theoperating time of the charged particle beam exposure apparatus, and thethroughput can be improved considerably.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a column structure of anexample of a conventional electron beam exposure apparatus;

FIG. 2 is a perspective view showing electromagnetic deflection coilsshown in FIG. 1;

FIGS. 3(A-C) shows measured results of deviation components of the beamposition when a main deflector is caused to generate heat continuously;

FIGS. 4 and 5 are diagrams for explaining the operating principle of thepresent invention;

FIG. 6 is a cross sectional view showing a first embodiment of a chargedparticle beam exposure apparatus according to the present invention;

FIG. 7 is a graph for explaining the operation of the first embodiment;

FIG. 8 is a system block diagram showing a second embodiment of thecharged particle beam exposure apparatus according to the presentinvention;

FIG. 9 is a diagram showing a third embodiment of the charged particlebeam exposure apparatus according to the present invention;

FIG. 10 is a system block diagram showing a fourth embodiment of thecharged particle beam exposure apparatus according to the presentinvention;

FIG. 11 is a diagram for explaining the limit of the compensation usinga single heater body;

FIG. 12 is a diagram showing a fifth embodiment of the charged particlebeam exposure apparatus according to the present invention;

FIG. 13 is a diagram for explaining the change in the deflection fieldof the fifth embodiment;

FIG. 14 is a diagram showing a sixth embodiment of the charged particlebeam exposure apparatus according to the present invention;

FIG. 15 is a circuit diagram showing an embodiment of a control circuit;and

FIG. 16 is a system block diagram showing a seventh embodiment of thecharged particle beam exposure apparatus according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a description will be given of the operating principle of thepresent invention, by referring to FIGS. 4 and 5.

FIG. 4 generally shows the construction of a charged particle beamexposure apparatus according to the present invention. Electromagneticdeflection coils 1 are arranged at positions surrounding an optical axisO, and a charged particle beam traveling along the optical axis O isdeflected by generating a magnetic field thereby. A heat source 2 isarranged in a vicinity of the electromagnetic deflection coils 1. Forexample, this heat source 2 may be made up of a noninductive coil whichis formed by a pair of twisted lines having the going and returningparts thereof twisted.

Heat Q1 is generated from the electromagnetic deflection coils 1 by acurrent which is applied to the electromagnetic deflection coils 1 forthe purpose of deflecting the charged particle beam. On the other hand,heat Q2 is generated from the heat source 2. A control circuit 3 carriesout a control so that a change in the heat Q1 is compensated by a changein the heat Q2.

By compensating the change in the heat Q1 generated by the currentapplied to the electromagnetic deflection coils 1 by the change in theheat Q2 which is generated from the heat source 2, it is possible tokeep the effect of the heat which is generated as a whole with respectto the charged particle beam constant.

FIG. 5 generally shows the change in the heat Q1 generated from theelectromagnetic deflection coils 1 and the change in the heat Q2generated from the heat source 2. When the heat Q1 is generated from theelectromagnetic deflection coils 1, the heat Q2 generated from the heatsource 2 is changed so as to cancel the change in the heat Q1.Accordingly, the total effect of the heat Q1 and the heat Q2 withrespect to the surrounding does not change and can be maintainedconstant.

For example, if the total amount of heat generated is constant, theeffect of the heat on the surrounding does not change even if thecurrent applied to the electromagnetic deflection coils 1 changes afterthe temperature change of the charged particle beam exposure apparatussaturates. For this reason, it is possible to prevent the drift of thecharged particle beam due to the temperature change.

Next, a description will be given of a first embodiment of the chargedparticle beam exposure apparatus according to the present invention, byreferring to FIGS. 6 and 7. FIG. 6 shows a cross section of the firstembodiment of the charged particle beam exposure apparatus, and FIG. 7is a graph for explaining the operation of the first embodiment.

In FIG. 6, an electromagnetic lens coil 11 is magnetically coupled to aniron yoke 12. Pole pieces 13 made of ferrite or the like aremagnetically coupled to the tip end of the iron yoke 12. A coil supportpart 14 is arranged on the inner side of the electromagnetic lens, andelectromagnetic deflection coils 16 are mounted on the outer side of thecoil support part 14.

Electrostatic deflection electrodes 17 are arranged at mutuallyconfronting positions on the inner side of the coil support part 14. Thenumber of electromagnetic deflection coils 16 and the number ofelectrostatic deflection electrodes 17 are shown in an abbreviatedmanner and does not necessarily correspond to the actual numbers so asto simplify the drawing. A heater body 10 is arranged in a vicinity ofthe outer side of the electromagnetic deflection coils 16. The heaterbody 10 is made of a resistor element, for example, and generates Jouleheat when a current is applied thereto. As shown in FIG. 7, this currentwhich is applied to the heater body 10 is controlled so that a sum ofthe heat Q2 generated from the heater body 10 and the heat Q1 generatedfrom the electromagnetic deflection coils 16 becomes a constant valueQ0.

In other words, if the heat Q1 generated from the electromagneticdeflection coils 16 changes as indicated by a solid line due to thecurrent applied to the electromagnetic deflection coils 16, a currentchange for compensating for this change is applied to the heater body10. Hence, the heat Q2 generated from the heater body 10 changes in theopposite direction to the change of the heat Q1 as indicated by a dottedline in FIG. 7, and the control is carried out so that the sum of theheat Q1 and the heat Q2 becomes the constant value Q0.

By the above described control, the heat Q0 which is generated from theelectromagnetic deflection coils 16 and the heater body 10 as a whole isalways maintained constant, and no temperature change occurs after thesystem once reaches the stable state.

When the charged particle beam is not irradiated on a wafer 19, it isdesirable to apply a predetermined current to the electromagneticdeflection coil 16 as indicated by the "start of exposure" in FIG. 7, sothat the generated heat Q1 is approximately one-half the total heat Q0and the heat Q2 generated from the heater body 10 is approximately thesame as the heat Q1.

Hence, by applying an idle current to the electromagnetic deflectioncoils 16 even when the charged particle beam is not irradiated on thewafer 19, it becomes possible to easily and quickly cope with the changein the current value regardless of the current value which is set whenirradiating the charged particle beam on the wafer 19.

If a large current is to be applied to the electromagnetic deflectioncoils 16, it is desirable from the point of view of making a stabletemperature compensation that a current is applied to the heater body 10to a certain extent.

The temperature of the pole pieces 13 and the like rises because theelectromagnetic deflection coils 16 and the heater body 10 as a wholealways generate a constant amount of heat. Correction data forcorrecting the astigmatism, focal point, distortion and the like of theoptical system are obtained in a state where the temperature rise hassaturated, and a correction using the correction data is carried out atthe time of the exposure.

FIG. 8 shows a second embodiment of the charged particle beam exposureapparatus according to the present invention. In this embodiment, thepresent invention is applied to an electron beam exposure apparatus.

In FIG. 8, a pattern generator 21 generates pattern data including aX-direction component and a Y-direction component. The X-directioncomponent is supplied to a digital-to-analog converter (DAC) 22a, andthe Y-direction component is supplied to a DAC 22b. Deflection data fromthe pattern generator 21 are also supplied to an analog operationcircuit 24.

Deflection data which have been converted into analog form are suppliedfrom the DACs 22a and 22b to respective electromagnetic deflection coildriving circuits 23a and 23b. The electromagnetic deflection coildriving circuits 23a and 23b generate driving currents for drivingelectromagnetic deflection coils 26.

The output signals of the DACs 22a and 22b are also supplied to theanalog operation circuit 24. The analog operation circuit 24 supplies acontrol signal corresponding to a(1-bX² -cY²)^(1/2) to a heater drivingcircuit 25, where "a" "b" and "c" denote correction coefficients whichare set so that the total amount of heat generated from theelectromagnetic deflection coils 26 and the compensation heater 27becomes constant, and X and Y respectively denote the X-direction andY-direction components. The heater driving circuit 24 generates acurrent corresponding to the amount of heat which is obtained bysubtracting the amount of heat generated from the electromagneticdeflection coils 26 from a predetermined value. The output current ofthe heater driving circuit 24 is supplied to a compensation heater 27.

The electromagnetic deflection coils 26 generate a magnetic field fordeflecting an electron beam EB, and also generate heat due to thecurrent which flows through the electromagnetic deflection coils 26. Thecompensation heater 27 changes the heater generated therefrom so as tocompensate for the change in the heat generated from the electromagneticdeflection coils 26.

In other words, the total amount of heat generated from theelectromagnetic deflection coils 26 and the compensation heater 27 ismaintained constant. For this reason, the effect of the heat to thesurroundings caused by the electromagnetic deflection coils 26 and thecompensation heater 27 does not change depending on the magnitude of thedeflection, and is maintained constant. The electron beam EB passesthrough a final aperture FA and is converged on the wafer W by aprojection lens 28. In addition, the electron beam EB is deflected to adesired position by the electromagnetic deflection coils 26.

The analog operation circuit 24 carries out an operation based on thepattern data so that the total amount of heat generated from theelectromagnetic deflection coils 26 and the compensation heater 27becomes constant, and supplies the control signal to the heater drivingcircuit 25.

Therefore, it is possible to prevent the beam position from drifting dueto the temperature change by maintaining the amount of heat generated inthe vicinity of the electromagnetic deflection coils 26 constant.

According to the conventional electron beam exposure apparatus, thedrift of the electron beam position caused by the heat generated fromthe electromagnetic deflection coils was approximately 0.3 μm even whenthe electromagnetic deflection coils were cooled. However, according tothis embodiment shown in FIG. 8, it was possible to reduce the drift ofthe electron beam position to approximately 0.05 μm.

FIG. 9 shows a third embodiment of the charged particle beam exposureapparatus according to the present invention. In FIG. 9, those partswhich are the same as those corresponding parts in FIG. 6 are designatedby the same reference numerals, and a description thereof will beomitted.

In this embodiment, a pair of coil support parts (hereinafter referredto as bobbins) 14a and 14b are arranged on the inner side of theelectromagnetic lens to form a double structure. That is, a cylindricalspace is defined by the inner bobbin 14b and the outer bobbin 14aand aflow passage 15 is formed in this cylindrical space. The electromagneticdeflection coils 16 are divided into two parts, one part being fixed tothe inner bobbin 14b and the other part being fixed to the outer bobbin14a. The flow passage 15 passes an intermediate part between the twoparts of the electromagnetic deflection coils 16.

The pattern generator 21 generates deflection data of the chargedparticle beam and supplies the deflection data to the DAC 22. The DAC 22supplies the deflection data to a main deflection amplifier 23a so as togenerate a current for driving the electromagnetic deflection coils 16.

The DAC 22 also supplies a signal corresponding to the deflection datato a heat compensation circuit 33, and variably sets a current i whichis supplied to a heater body 34.

The heater body 34 is arranged within a coolant passage through which acoolant 31 flows. The coolant 31 which has made contact with the heaterbody 34 is supplied to the flow passage 15 within the electromagneticlens via a coolant passage 32. This coolant 31 is supplied at a constantspeed, but the current i which is supplied to the heater body 34 fromthe heater compensation circuit 33 is controlled by the deflection dataand the cooling capacity is changed thereby. The current i is adjustedso that the sum of the heat generated from the electromagneticdeflection coils 16 in the vicinity of the electromagnetic lens and theheat from the coolant 31 becomes constant.

For this reason, the total amount of heat which is generated in thevicinity of the electromagnetic lens is maintained constant, similarlyto the embodiment shown in FIG. 6. As a result, the temperature in thevicinity of the electromagnetic lens is maintained constant regardlessof the magnitude of the deflection.

FIG. 10 shows a fourth embodiment of the charged particle beam exposureapparatus according to the present invention. In FIG. 10, those partswhich are the same as those corresponding parts in FIG. 8 are designatedby the same reference numerals, and a description thereof will beomitted.

In this embodiment, the output signal of the pattern generator 21 isalso supplied to DACs 22c and 22d. Signals from these DACs 22c and 22dcorresponding to the amounts of deflection of the charged particle beamin the X and Y directions are supplied to the analog operation circuit24.

Since the signals supplied to the electromagnetic deflection coildriving circuits 23a and 23bare independent from the signals supplied tothe analog operation circuit 42, it is possible to prevent the datawhich is used to deflect the charged particle beam from being affectedwhen the amount of heat generated from the compensation heater 27 iscontrolled.

In addition, it is easier to adjust the current which is supplied to thecompensation heater 27 independently of the signals which are applied tothe electromagnetic deflection coils 26.

In the embodiments described heretofore, a single heater body isarranged in the vicinity of the electromagnetic deflection coils.However, the heater body and the electromagnetic deflection coils arelocated at mutually different positions, and there are time differencesamong the times required for the heat generated from the heater body andthe heat generated from the electromagnetic deflection coils to betransferred to the pole pieces. When compensating for the change in theheat generated from the electromagnetic deflection coil by the change inthe heat generated from the heater body, a deviation is introduced dueto the time differences of the heat transfers in the transient state ifa single heater body is used, and the compensation of the change of theheat generated from the electromagnetic deflection coil becomes limited.

For example, if the current value supplied to the electromagneticdeflection coil is greatly changed, it is difficult to completelycompensate for the change in the heat generated from the electromagneticcoil by the heat generated from the heater body.

FIG. 11 generally shows the limit of the compensation using a singleheater body. In FIG. 11, the abscissa indicates the time in seconds, andthe ordinate indicates the change of the deflection field, that is, thechange in the position to which the electron beam is actually deflectedin response to the same deflection data. For example, the ordinateindicates the amount of drift of the field center.

In FIG. 11, P0 indicates the total change which is the sum of thechanges caused by the heat generated from the electromagnetic deflectioncoils and the heat generated from the heater body. It is assumed for thesake of convenience that the current value supplied to theelectromagnetic deflection coil is greatly changed at a time t=0.

In addition, P1 indicates the change in the deflection field when nocurrent is supplied to the heater body and the electromagneticdeflection coils generate the heat. Furthermore, P2 indicates the changein the deflection field when no current is supplied to theelectromagnetic deflection coil and the a current is supplied only tothe heater body.

The deflection current supplied to the electromagnetic deflection coiland the compensation current supplied to the heater body are selected tosuch value that the deflection field does not change after asufficiently long time elapses. However, even though the deflection andcompensation currents are so selected, a change occurs in the deflectionfield in the transient state. FIG. 11 shows a case where the deflectionfield dips, but the deflection field may rise depending on thearrangement of the heater body.

By providing the heater body and compensating for the change in theamount of heat generated from the electromagnetic deflection coils bythe change in the amount of heat generated from the heater body, it ispossible to greatly reduce the change in the deflection field. But it isextremely difficult to completely prevent the deflection field fromchanging also in the transient state.

Next, a description will be given of other embodiments of the chargedparticle beam exposure apparatus according to the present inventionwhich can sufficiently prevent the deflection field from changing in thetransient state.

FIG. 12 shows a fifth embodiment of the charged particle beam exposureapparatus according to the present invention. In FIG. 12, those partswhich are the same as those corresponding parts in FIG. 6 are designatedby the same reference numerals, and a description thereof will beomitted.

In this embodiment, three heater bodies 27a, 27b and 27c which arearranged in the vicinity of the electromagnetic deflection coils 16 atpositions distributed above and below the effective center of theelectromagnetic deflection coils 16. In addition, a control circuit 39which includes heater driving circuits 41, 42 and 43 for independentlysupplying currents to the heater bodies 27a, 27b and 27c is provided asshown in FIG. 12.

Deflection data Mx and My of the electromagnetic deflection coil 16 aresupplied to the electromagnetic deflection coil driving circuits (notshown) and to a calculation circuit 37 which calculates the amount W ofheat generated from the electromagnetic deflection coil 16.

A calculation circuit 38 calculates the amount of heat to be generatedby the heater bodies 27a, 27b and 27c by subtracting the amount W ofheat generated from the electromagnetic deflection coils 16 from apredetermined amount Wo of heat which is to be generated. The calculatedamount of heat to be generated by the heater bodies 27a, 27b and 27c issupplied to the control circuit 39, and the control circuit 39 obtainsthe amount of heat to be generated by each of the heater bodies 27a, 27band 27c based thereon. The driving circuits 41, 42 and 43 supplycurrents which are based on the calculation to the heater bodies 27a,27b and 27c so as to generate heat.

The heater bodies 27a, 27b and 27c are arranged in the vicinity of theelectromagnetic deflection coils 16, but the positions thereof mutuallydiffer. Hence, the transfer characteristic with which the heat istransferred to the pole pieces 13 of the electromagnetic lens differ foreach of the heater bodies 27a, 27b and 27c.

Accordingly, by adjusting the amounts of heat to be generated from theheater bodies 27a, 27b and 27c, it is possible to set the effective heattransfer time of each of the heater bodies 27a, 27b and 27c identical tothose of the electromagnetic deflection coils 16, so as to adjust theeffects of the heat to the surrounding parts such as the pole pieces 13.As a result, it is possible to maintain the total effect of the heat onthe surrounding parts constant even in the transient state as shown inFIG. 13. In FIG. 13, P2, P3 and P4 respectively indicate the independenteffects of the heater bodies 27a, 27b and 27c on the change of thedeflection field.

Therefore, this embodiment can further reduce the change in thedeflection field in the transient state by arranging the plurality ofheater bodies in the central part of the electromagnetic deflectioncoils at mutually different positions along the optical axis, and bysetting mutually different heat transfer characteristics to the heaterbodies.

FIG. 14 shows a sixth embodiment of the charged particle beam exposureapparatus according to the present invention. In FIG. 14, those partswhich are the same as those corresponding parts in FIG. 9 are designatedby the same reference numerals, and a description thereof will beomitted. In this embodiment, a coolant is used as in the case of theembodiment shown in FIG. 9, and a plurality of heater bodies arearranged in the flow passage on the inner side of the electromagneticlens.

In FIG. 14, electromagnetic deflection coils 16(X) and 16(Y) arearranged within the flow passage 15 which is formed by the coil supportparts 14a and 14b. In addition, two heater bodies 34a and 34b arerespectively arranged within the flow passage 15 in the vicinity of theelectromagnetic deflection coils 16(X) and 16(Y) above and below theelectromagnetic deflection coils 16(X) and 16(Y) along the optical axis.

The pattern generator 21 supplies the deflection data of the chargedparticle beam to the DAC 22, and the DAC 22 supplies the driving currentto the electromagnetic deflection coils 16 via the main deflectionamplifier 23a. The DAC 22 also supplies the deflection data to a heatcompensation circuit 33a. The heat compensation circuit 33a generatescurrents i₁ and i₂ which are respectively to be supplied to the heaterbodies 34a and 34b based on the deflection data.

The heater bodies 34a and 34b are arranged at positions within the flowpassage 15 having mutually heat transfer characteristics with respect tothe pole pieces 13. Hence, the effects of the heat generated from theheater bodies 34a and 34b with respect to the surrounding parts such asthe pole pieces 13 are mutually different. By adjusting the amounts ofheat generated from the heater bodies 34a and 34b, it is possible toreduce the change in the deflection field in the transient state,similarly as in the case of the embodiment shown in FIG. 12.

FIG. 15 shows an embodiment of a control circuit which can independentlycontrol the currents which are to be supplied to a plurality of heaterbodies. In FIG. 15, it is assumed for the sake of convenience that fourheater bodies 24a, 24b, 24c and 24d are provided, and that the currentsare supplied from four current sources 41a, 41b, 41c and 41d.

The current sources 41a, 41b, 41c and 41d are voltage-current convertercircuits which convert an input voltage into a current value, andrespectively have variable resistors VR1, VR2, VR3 and VR4 connected toan input end thereof. The variable resistors VR1, VR2, VR3 and VR4 areconnected in series, and one end of this series connection is groundedwhile the other end of this series connection receives a signalproportional to (Wo-W).

In other words, (Wo-W) is a signal proportional to the amount of heatwhich is to be generated from the heater bodies 27a, 27b27c and 27d as awhole. The ratio of the amounts of heat to be generated by the fourheater bodies 27a through 27d can be variably adjusted by adjusting thevariable resistors VR1 through VR4 to make a transient effect on thecharged particle beam a minimum when the currents supplied to theelectromagnetic deflection coils.

In the embodiments shown in FIGS. 12 and 14, for example, the amount ofheat to be generated by the plurality of heater bodies as a whole may bederived theoretically, but it is more desirable to determine the amountof heat experimentally.

For example, currents are independently supplied to each of theplurality of heater bodies, and a change in the deflection field whichoccurs in this case is measured. In addition, the change in thedeflection field is measured for various deflection data. Then, theratio of the amounts of heat to be generated by each of the heaterbodies in order to carry out the compensation is obtained based on thedeflection data. Moreover, currents are actually supplied to theelectromagnetic deflection coils and the heater bodies so as to obtainthe changes thereof, and the current values to be supplied to each ofthe heater bodies are finally determined.

When carrying out the compensation by the heat generated from the heaterbodies, the temperature of the entire system rises. Hence, it isdesirable to adjust each part of the structure so that the astigmatism,focal point correction, distortion correction and the like of theoptical system can be made in the state where the temperature has risen.

Even if the heater body generates a slight magnetic field, the currentwhich flows through the heater body is synchronized to the currentsetting of the main deflector, and the heat compensation is made at thetime of each kind of correction map measurement. For this reason, theerror in the beam position and the focal error caused by the magneticfield generated by the heater body are taken into account in thecorrection map.

With respect to the time lag of the temperature change caused by theheat transfer, it is possible to take the following measures. That is,the heater bodies are divided into at least in two parts respectivelyabove and below the central part of the main deflector along the opticalaxis. In addition, the amounts of heat generated by the heater bodies ofthe two parts are adjusted so that the effects of the heat generatedfrom the heater bodies and the coils of the main deflector on thesurrounding parts such as the pole pieces are made equivalent betweenthe two parts. Hence, the effects of the heat transfer can be madeequivalent between the two parts.

Accordingly, the temperature inside and outside the main deflector canalways be maintained constant during the exposure and during theadjustment, and the surrounding parts such as the pole pieces will notchange in position or dimension due to thermal expansion. As a result,the beam position and focal position are always stably determined,thereby making it possible to draw the patterns with a high accuracy.

of course, the number of heater bodies is not limited to 3, and it ispossible to provide 2 or more than 3 heater bodies.

FIG. 16 shows a seventh embodiment of the charged particle beam exposureapparatus according to the present invention. In FIG. 16, those partswhich are the same as those corresponding parts in FIG. 8 are designatedby the same reference numerals, and a description thereof will beomitted. In this embodiment, two heater bodies 27a and 27b are provided.

As shown in FIG. 16, two analog operation circuits 24a and 24b and twoheater driving circuits 25a and 25b are respectively provided to drivethe heater bodies 27a and 27b. The analog operation circuit 24a suppliesa control signal corresponding to a₁ (1-bX² -cY²)^(1/2) to the heaterdriving circuit 25awhere "a₁ 38 denotes a correction coefficient Theanalog operation circuit 24b supplies a control signal corresponding toa₂ (1-bX² -cY²)^(1/2) to the heater driving circuit 25bwhere "a₂ "denotes a correction coefficient.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

What is claimed is:
 1. A charged particle beam exposure method fordeflecting a charged particle beam in a deflection system which includeselectromagnetic deflection coils, said charged particle beam exposuremethod comprising the steps of:(a) controlling the deflection systembased on deflection data including currents applied to theelectromagnetic deflection coils; and (b) generating heat based ondeflection data including said currents applied to the electromagneticdeflection coils in at least a vicinity of the electromagneticdeflection coils so as to compensate for a change in heat generated fromthe electromagnetic deflection coils.
 2. The charged particle beamexposure method as claimed in claim 1, wherein said step (b) generatesthe heat by controlling heat source means arranged in the vicinity ofthe electromagnetic deflection coils.
 3. The charged particle beamexposure method as claimed in claim 2, wherein said step (b) controlsthe heat source means so that a total amount of heat generated from theelectromagnetic deflection coils and the heat source means isapproximately constant.
 4. The charged particle beam exposure method asclaimed in claim 2, wherein said step (a) supplies a constant current tothe electromagnetic deflection coils even during a time in which noirradiation of the charged particle beam on an exposure surface is made.5. The charged particle beam exposure method as claimed in claim 4,wherein said step (a) supplies a current to the electromagneticdeflection coils and to the heat source means even during a time whensaid deflection data is not received.
 6. The charged particle beamexposure method as claimed in claim 2, wherein said step (b) uses aheated fluid which flows at a constant flow rate as the heat sourcemeans.
 7. The charged particle beam exposure method as claimed in claim2, wherein said step (b) uses a single heater which is arranged in thevicinity of the electromagnetic deflection coils.
 8. The chargedparticle beam exposure method as claimed in claim 2, wherein said step(b) uses a plurality of heaters which are arranged in the vicinity ofthe electromagnetic deflection coils.
 9. A charged particle beamexposure method for deflecting a charged particle beam in a deflectionsystem which includes electromagnetic deflection coils, said chargedparticle beam exposure method comprising the steps of:(a) controllingthe deflection system based on deflection data; and (b) generating heatin at least a vicinity of the electromagnetic deflection coils so as tocompensate for a change in heat generated from the electromagneticdeflection coils, wherein said step (b) generates the heat bycontrolling heat source means arranged in the vicinity of theelectromagnetic deflection coils; and wherein the heat source meansincludes an electrical resistance, said step (a) supplies a current tothe electromagnetic deflection coils, and said step (b) supplies to theelectrical resistance a current which changes approximately insynchronism with a change in the current supplied to the electromagneticdeflection coils by said step (a).
 10. A charged particle beam exposuremethod for deflecting a charge particle beam in a deflection systemwhich includes electromagnetic deflection coils, said charged particlebeam exposure method comprising the steps of:(a) controlling thedeflection system based on deflection data including currents applied tothe electromagnetic deflection coils; (b) generating heat in at least avicinity of the electromagnetic deflection coils so as to compensate fora change in heat generated from the electromagnetic deflection coils,wherein said step (b) generates the heat by controlling heat sourcemeans arranged in the vicinity of the electromagnetic deflection coils,wherein said step (b) uses a plurality of heaters which are arranged inthe vicinity of the electromagnetic deflection coils; and (c) obtainingbeforehand a ratio of the amounts of heat to be generated by theplurality of heaters which makes a transient effect on the chargedparticle beam a minimum when the currents supplied to theelectromagnetic deflection coils in said step (a) change.
 11. A chargedparticle beam exposure apparatus comprising:a deflection systemincluding electromagnetic deflection coils for deflecting a chargedparticle beam; heat source means arranged in a vicinity of theelectromagnetic deflection coils for generating heat; and control meansfor controlling said heat source means based on currents applied to theelectromagnetic deflection coils, so as to compensate for a change inheat generated from the electromagnetic deflection coils by the heatgenerated from said heat source means.
 12. The charged particle beamexposure apparatus as claimed in claim 11, wherein said control meanscontrols said heat source means so that a total amount of heat generatedfrom the electromagnetic deflection coils and said heat source means isapproximately constant.
 13. The charged particle beam exposure apparatusas claimed in claim 11, which further comprises driving means forsupplying a constant current to the electromagnetic deflection coilseven during a time in which no irradiation of the charged particle beamon an exposure surface is made via said deflection system.
 14. Thecharged particle beam exposure apparatus as claimed in claim 13, whereinsaid driving means supplies a current to the electromagnetic deflectioncoils and to the heat source means even during a time when deflectiondata is not received.
 15. The charged particle beam exposure apparatusas claimed in claim 11, wherein said heat source means includes meansfor heating a fluid, and means for flowing the heated fluid at aconstant flow rate.
 16. The charged particle beam exposure apparatus asclaimed in claim 11, wherein said heat source means includes a singleheater which is arranged in the vicinity of the electromagneticdeflection coils.
 17. The charged particle beam exposure apparatus asclaimed in claim 11, wherein said heat source means includes a pluralityof heaters which are arranged in the vicinity of the electromagneticdeflection coils.
 18. The charged particle beam exposure apparatus asclaimed in claim 17, wherein said control means controls the heatgenerated from said heat source means based on an anticipated amount ofheat to be generated from the electromagnetic deflection coils.
 19. Acharged particle beam exposure apparatus comprising:a deflection systemincluding electromagnetic deflection coils for deflecting a chargedparticle beam; heat source means arranged in a vicinity of theelectromagnetic deflection coils for generating heat; and control meansfor controlling said heat source means based on currents applied to theelectromagnetic deflection coils, so as to compensate for a change inheat generated from the electromagnetic deflection coils by the heatgenerated from said heat source means, wherein said control meanssupplies to said heat source means currents which change respectivelyapproximately in synchronism with a change in the currents supplied tothe electromagnetic deflection coils.
 20. A charged particle beamexposure apparatus comprising:a deflection system includingelectromagnetic deflection coils for deflecting a charged particle beam;heat source means arranged in a vicinity of the electromagneticdeflection coils for generating heat, wherein said heat source meansincludes a plurality of heaters which are arranged in the vicinity ofthe electromagnetic deflection coils; and control means for controllingsaid heat source means based on currents applied to the electromagneticdeflection coils, so as to compensate for a change in heat generatedfrom the electromagnetic deflection coils by the heat generated fromsaid heat source means, wherein said control means controls theplurality of heaters based on a ratio of the amounts of heat to begenerated by the plurality of heaters which makes a transient effect onthe charged particle beam a minimum when the currents supplied to theelectromagnetic deflection coils change.